System for synchronizing series of recurring pulse emissions



MUssELMAN 2,646,510

3 Sheecs--SheeiI l #ENCE SYSTEM FOR SYNCHRONIZING SERIES OF RECURRING PULSE EMISSIONS Original Filed June 13, 1945 July 2l, i953 rmm ATTORNEY july 21, E953 G. H. MUssELMAN 25,646,510

SYSTEM FOR SYNCHRONIZING SERIES oF RECURRING PULSE EMISSIONS Original Filed June 13,' 1945 5 Sheets-Sheet 2 FIG. 2

INVENTOR GLENN H. MUSSELMAN ATTORNEY Juiy 21, w53 G. I-I. MUSSELMA 2,646,519

. SYSTEM FOR SYNCHRONIZING ERIES OF RECURRING PULSE EMISSZEONS Original Filed June 13, 1945 y 5 Sheets-Sheet 5 BEGINNING OF' VIDEO PULSE OUTPUT O OUTPUT OF GENERATOR s(GENERATOR 2e 27 g I SOM SEC. I OELAYI T-'J DIII DDUE-QC, VIBR TOR MUI TI 25 VIBRATOR 24 l I' OUTPUT OUTPUT OF MIXER OF MIXER 2s 29 TIME INVENTOR l GLEN N H. MUSSELMAN ATTO R N EY Patented July 2l, 1853 UHTE SYSTEM FOR SIYNCHRNIZINGSERIES F RECURRING FULSE EMISSIQNS Glenn H. Musselman, Boston, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy (Cl. Z50-36) 1.0 Claims. l

This invention relates toa means for maintaining a `recurrent series of pulse emissions from `a rst radio transmitter in a known -time relation with a similarly recurrent Series of pulse emissions from a second radio transmitter.

In patent application Serial No. 599,163 led June 13, 1945 of J. A. Pierce, D. E. Kerr, and J. C. Street is disclosed a long range navigation system which enables a navigator to locate himself on the surface of the earth. This ksystem comprises broadly two pairs of spaced pulse transmitters, one transmitter of each pair preferably although not necessarily having the same location, and a receiver for the pulses with the necessary timing equipment at the point to be located. The diiierence in arrival time of corresponding pulses from each pair of transmitters is measured. With this information and information as to the time relation of the corresponding pulses from each pair of transmitters a location may be established along two spherical hyperbolas having their foci at respective pairs of transmitters. The intersection of these hyperbolas will x the position o1 the receiver.

Obviously each pair of stations must have corresponding pulses emitted in a xed time relation known to the navigator at the receiver, that is the time delay between corresponding p-ulses must be maintained xed. It iollows as a corollary that the pulse emissions from each transmitter of a pair must have the same recurrence rate, and if the recurrence rate at the controlled or slave transmitter is held to that of the controlling or master transmitter once the time relation has been established. Each pair of transmitters may be identied by the navigator at 'the receiver, and he knowing the time relation may determine his position on the earth.

it is accordingly an object of this invention to provide apparatus for maintaining a recurrent series of pulse emissions `from a first radio transmitter in a known time relation with a similarly recurrent series of pulse emissions from a second radio transmitter.

It is a further object of this invention to provide apparatus for maintaining a recurrent series of pulse emissions from a first radio transmitter in 'a known time relation with a 'similarly recurrent series of lpulse emissions from a 'second'radi'o transmitter by controllingl the recurrence frequency of theiirst radio transmitter.

Qther and further objects will be apparent during the course vof 'the following description together with Lt'he accompanying-drawings where:

4Fig. l'isabloc'k diagram oran embodiment .of

the invention;

Fig. 2 is a circuit diagram showing details-of certain blocks o'f Fig. 1; and

Fig. 3 discloses `graphs of certain wave forms occurring in the invention.

The block diagram of Fig. 1 disclosestheinvention incorporated in a pulse transmitter of th'e type disclosed in the above-mentioned vapplication. This transmitter is being used as a fslave and Will be described only in sufcientvdetail for comprehension of the principles of the vinstant invention, a more complete description lbeing given in the above-mentioned application. A timing wave is obtained from a timing 'wave vgenerator Ill, which is controlled by a crystal which may although not necessarily, be kept in a constant temperate oven to insure an output extremely stable in frequency. The output from generator Ii) after being squared in squaring amplifier Il is applied to counter I2 where the frequency is reduced by the desired amount, say from 100 kilocycles to cycles. The output of counter I2 is applied to square Wave generator I3, which produces a square wave of one halfv the input frequency, namely 25 cycles. This square wave is conveyed to A delay multivibrator ill and B delay multivibrator I5. Multivibrator I4 is triggered by the leading edge of the positive half of the square wave and multivibrator I5 is triggered by the leading edge of the negative half of the square wave. The delays of both multivibrators 'are adjustable over a range sufficient to permit the difference in time of occurrence between the outputs of the multivibrators to r'equal the known time interval. The trailing 'edges of Amultivibrators I4 and I 5 are each utilized to trigger pedestal generator i6 which produces a rectangular voltage wave of a duration exceeding the width of the emission pulses. The leading and trailing edges of the pedestal wave are utilized to turn on and oi respectively vthe sweep voltage of `fast sweep generator I7 which is impressed on the horizontal plates of a cathode ray tube 'in indicator IS. Transmitter I9 is triggered in response to the trailing 'edge of the output wave vofmultivibrator I5, and a recurrent series of pulses vare emitted from antenna 20, which are the "slave signals. These pulse emissions as well as `the series of pulse emissions from the "master station are picked upy by antenna 2I. Electronic attenuator 22 operates in response to the output of square wave generator I3 to attenuate .the slave pulse emission received With respect to the master pulse emission received, when the slave station is properly phased. This perm-its substantially equal pulse emissions .from the frnaster and slave stations to be applied to receiver 23. The output of receiver 23 is applied to the vertical plate of a cathode ray tube in indicat-or I8. With the slave station properly phased the pulses from the master and slave stations will appear on their respective sweeps in substantial coincidence, and Will so remain if the recurrence frequency of the slave station is maintained the same as that of the master station. This recurrence frequency of the slave station may be maintained by manual adjustment, but an automatic adjustment is obviously more desirable.

To obtain an automatic adjustment the output of multivibrator I4 is also fed to an adjustable delay multivibrator 24 which has a delay range of 20 to 60 microseconds and which operates in response to the trailing edge of the wave from multivibrator i4. The outputs from multivibratorv 24 are applied to two gate generators 2S and 2l', one output being first passed through a 50 microsecond preset delay multivibrator 2t to further delay'this output. Gate generators 2t and 21 each produce a narrow pulse of the order of microseconds in response to the trailing edges of the output waves from multivibrators 24 and 25. These narrow pulses from their respective generators are impressed on mixers 23 and 29. The output Video pulses from receiver 23 are also impressed on mixers 28 and 29 through cathode follower 34.

Mixers 28 and 29 whose circuits are described in more detail with reference to Fig, 2 produce each a pulse whose magnitude depends on the coincidence of the narrow pulses from gate generators 2t and 21 on the leading and trailing edges respectively of the video pulse. The mixers are rendered operative by the narrow pulses, and ii a video pulse is also impressed on the mixers at this time, the output wave from the mixer will depend on the amplitude of the video pulse at this time. This may be seen more clearly in Fig. 3 where the A line represents a video pulse having a width of about 70 microseconds. The B line represents the narrow pulses applied to the mixer. Assuming the slave station is adjusted to proper phase, the time of occurrence of the leading narrow pulse from generator 2t Will be determined by multivibrator 24, and the time of occurrence of the lagging narrow pulse from generator 2l' with reference to the leading narrow pulse will be determined by multivibrator 25. The mixer outputs on line C are pulses occurring at the same times as the narrow pulses from generators 25 and 27 and have a magnitude depending on that of the Video pulse at these times. Multivibrator 24 is adjusted to have the leading narrow pulse occur substantially on the mid-portion of the leading edge of the video pulse and multivibrator 25 is adjusted to have the lagging narrow pulse occur substantially on the mid-portion of the trailing edge of the video pulse. It is apparent that when the narrow pulses are symmetrical or coincident with respect to the video pulse, that is, when the narrow pulses occur on corresponding positions on the leading and trailing edges of the video pulse, the output pulses from the mixer will be equal assuming the mixers are balanced, but when the narrow pulses lead or lag from the symmetrical position, the output mixer pulses will be unequal. When the narrow pulses lead the video pulse the output of mixer 28 will be decreased and the output from mixer 29 will be increased, and vice versa.

Integrating circuits 3B and 3l are provided to produce each a relatively steady voltage depending on the magnitude of the output pulses from the respective mixers. To secure a voltage indication of the difference in the magnitudes oi" the steady voltages from the integrating circuits a differential amplifier 32 is used, whose output voltage will deviate from a reference level in an amount and direction determined by the difierence in magnitude of steady voltages. The voltage from the differential amplier controls a reactance tube circuit 33 by varying the reactance or" this circuit in accordance with the magnitude of the voltage. The reactance of circuit 553 is in parallel with the tank circuit of the timing wave generator Iii. A change in this reactance will be suflicient to pull the frequency or the timing wave in a direction depending on the direction ci the reactance change.

Thus the frequency oi the timing wave will be changed in accordance with any deviation oi the narrow pulses produced by gate generators 2S and 2l from a symmetrical or coincident position in time with reference to the video pulse from the master station. The ychange in frequency will be in such a direction as to reduce the deviation, that is, to tend to restore the symmetrical position or coincidence, and the pulse emissions of the slave station will be substantially maintained in a desired and known time relation with the pulse emissions from the master station. Also the recurrence rate of the pulse emissions from the slave station will be maintained the same as the recurrence rate of the pulse emissions from the master station. The known time interval will in the main be determined by the delay settings of multivibrators Il and I5 with due regard for the fact that multivibrator I5 is triggered later by one hali` cycle oi square wave generator i3. Multivibrator 22 is adjustable over a relatively small range, and is used to compensate for the diiierence in time between the beginning of the master video pulse and the begining of leading narrow pulse from generator 2G.

In the circuit diagram of Fig. 2 the voltage wave from multivibrator Id is applied at terminal 35 connected through a peaking condenser 3S to adjustable delay multivibrator 243. VThis multi- Vibrator is of a'known type, and comprises two tubes 24d and 2419. Tubes 2da and 24h are normally in the non-conducting and conducting state respectively. A negative peaked voltage, corresponding to the trailing edge oi the output wave from multivibrator I4, applied to the grid of tube 24h will bias this grid beyond cutoi to render tube 24h non-conducting. This will cause the cathode voltage of tube 2da to drop until this tube becomes conducting, with its plate potential dropping to maintain the grid of tube 2th biased below cutoff. This condition Ywill persist until condenser 35 has charged suiciently to permit the grid of tube 24h to rise above cutoff, when tube 24h once more conducts. The result oi this cycle is a positive gate being impressed on preset delay multivibrator 25. The time required to charge condenser 36 is determined by the setting of potentiometer 3l, which thus controls the delay setting of multivibrator 25.

Preset delay multivibrator 25, is similar in type to multivibrator 24 and operates inresponse to the neg-ative trailing edge of the wave impressed thereon from multivibrator 24. Potentiometer 38 determines its delay setting. Narrow gate generators 2S and 2'I have'their tubes 26a and 21a normally in the conducting state. The outputs from multivibrators 24 and 25 are conveyed to the grids of these tubes through peaking condensers 39 and 40. The negative trailing edge of the waves from these multivibrators will produce a negative peak voltage at .the grid lof tubes 26a :and 21a to bias them :below cutoff .to result in a narrow clipped positive pulse at the plate of each tube. Condenser 39 'is made `adjustable to permit proper balancing of the width ofthe respective narrow pulses.

These narrow pulses are applied to the respective grids of tubes 28a and 29a in mixers 28 and 2S to render these tubes conducting for the duration of ithe narrow pulse, fthe-'grids being-normally biased beyond cutoif. 'The video pulse .is applied in positive form 'at terminal 2H and after vpassing through cathode follower 3e 'Lisapplied to `the screens of both `tubes 28a and 2811.- If veitlier or both of these -tubes are 'inthe conducting state due Yto the narrowpulsesbe'ing:impressed on their grids, the plate voltage of the tubes 4will .drop further `by an amount dependingon theheight 'of the video pulse at the-occurrence of 'the narrow pulse applied Yto 'the particulartube. The'ne'gative voltage pulses -at'the `plates of the Atubes "at 28a and 29a are impressed on theirrespectiveiintegrating circuits 3B and 3L Integrating circuit 39 -includes a diodea'and-a condenser-32. The negative pulseimpressed attire-cathode of diode 30a flows therethrough to charge condenser d2. The rectifying action of the diode prevents 'the condenser from dischargingexcept slowly .through the resistors in series therewith. Thus the voltage impressed on theigrid of tub'ezaofidiiferential Lamplifier 32 will be steady except for "the slower change ldepending lon the magnitude of the negative pulses Afrom mixer 28. Integrating circuit l3| produces likewise a 'steady voltage ldependent only on the magnitude Yof the negative pulses Vvfrom mixer 29.

Since thevoltageonthe grid of ytube .32a rises as the voltage on `the grid of .tube 32h falls and vice `versa in diierential amplifier 32, the voltage at the 4plate of tube 32a 'will rise and fall in accordance with the .di'iference between the two grid voltages. This ydiierence voltage is 'tapped oi at the arm of potentiometer 44, whose resistance is connected 'between the plate'of tube 32a and a negative potential. The arm is adjusted so that whenthegridsof tubes 3.2a'and 32h have equal potentials, no potential -exists between the arm and ground. Whenithe .potentials on these grids are unbalanced, la positive :or negative direct voltage is conveyed to reactance tube circuit 33 connected to terminal "45 depending on the direction of the'unbalance.

l.'Lhe'level of the 'voltagesifed'to the differential amplier vwill -vary -due to noise 4and fading.. However, the diierence of these voltages will remain reasonably-stable during noise and fading, and be influenced mainly only by deviation in the slave station from the -desired time relation. Since the voltage fed lto lreactance tube circuit 33 depends only on the difference in voltage levels, this invention has the advantage of lreducing the adverse effects of 'noise and vfading to a, minimum. 1

The invention is to be limited 'only by -the scope of the 'appended claims.

I claim:

l. A means Vfor maintaining Va recurring-series of pulse emissions from a first radio transmitter in a known time relation with a similarly recurrent series-of pulse emissions'from a second radio transmitter comprising, vmeans for generating a timing wave'to control `therecurrence rate fofsaid first series of pulse emissions, .means `for producing a series of pairs `of `pulses 'ofthe same-recurrence rate as saidfirst pulseemissionseachpair of pulsesleadingthe Vcorresponding pulse of said rstseries .of pulse emissions by said known time interval, and means responsive to the deviation of said pair of pulses from coincidence with .the corresponding pulse of said second series of pulse emissions to control the frequency of said timing wave generating means to reduce said deviation.

y 2. A means for maintaining a recurrent series of pulse emissions from a first radio transmitter in a known time relation with a similarly recurrent series of pulse emissions from a second radio transmitter comprising, means for generating a timing wave to control the recurrence rate of said rst series of pulse emissions, means for producing aseries of pairs of pulses of the same recurrence rate as said rst pulse emissions, each pair of pulses leading a corresponding `pulse of said iirst series by said known time relation, means for producing a voltage depending on the deviation of said pair of pulses from a symmetrical occurrence with respect to the corresponding pulse of said second series of pulse emissions, and means responsive to said voltage to control the frequency of said timing wave generating means to reduce said deviation,

- 3. A means for maintaining a recurrent series of pulse emissions from a first radio transmitter in a known time relation with a similarly recurrent series of pulse emissions from a second radio transmitter comprising, means for generating a timing wave to control the recurrence vrate of said first series of pulse emissions, means for producing a series of pairs of pulses of the same recurrence rate as said first pulse emissions, each pair of pulses leading the corresponding pulse of said first series of Apulse emissions by the known time interval 'and each pair being separated in time less than the pulse width of said second series of pulse emissions, means producing a voltage depending on the deviation of said pair from a symmetrical position with respect to the leading and trailing edges of the corresponding pulse of said second series of pulse emissions, and a reactance tube circuit responsive to said voltage and operative to change the frequency of said timing wave generating means to reduce said deviation.

4. A means for maintaining` a recurrent series of pulse emissions from a first radio transmitter in a known time relation with a similarly recurrent series of pulse emissions from a second radio transmitter comprising, a timing wave generator to control the recurrence rate of said first series of pulse emissions, means for producing a series of narrow pulses of the same recurrence rate as said first pulse emissions, means for producing a second series of narrow pulses, each pulse of the second series being delayed from the first series byan amount less than the pulse width of said second series of pulse emissions to produce a series of pairs oi narrow pulses, each pair of narrow pulses leading by the known time relation the corresponding pulses of the iirst series of pulse emissions, a first mixer for said irst series of narrow pulses and said second series of pulse emissions, a second mixer for said second series oi narrow pulses and said second series of pulse emissions, the output oi said first mixer being a pulse, the amplitude oi which depends on the relative time of occurrence of anarrow ypulse oi said iirst series and a pulse of said second series oi pulse emissions, the output of said second mixer being a pulse, the amplitude of which depends on the relative time of occurrence of a narrow pulse of said second series and a pulse of said second series of pulse emissions, the output pulses of said two mixers beingr of substantially equal amplitude when the undelayed and delayed narrow pulses in a Apair occur in the leading and trailing edges, respectively, of a pulse of said second series of pulse emissions, first and second integrating circuits responsivev to said outputs of said first and second mixers, respectively, each integrating circuit producing an output voltage depending on the magnitude of respective mixer output pulses, a differential amplifier to produce a voltage whose magnitude depends on the difference in magnitudes of the output voltages of said integrating circuits, a reactance tube circuit responsive to the output of said differential amplifierand adapted to control the frequency of said timing wave generator, whereby the frequency of said timing wave generator may be controlled in accordance with the occurrence of said pair of pulses on the leading and trailing edges of corresponding pulses of said second series of pulse emissions;

5, A system for maintaining a recurrent first series of pulse signals in a known time relation with a similarly recurrent second series ci pulse ignals comprising, means for generating said first series of pulse signals at substantially the same recurrence rate as said sec-ond series oi pulse signals, means for generating a rst signal of the same recurrence rate as said first series of pulse signals, said signal leading a corresponding pulse of said first series by said vknown time relation, a time interval measuring circuit having as input signals thereto said first signal and pulses in said second series for producing a second signal having a characteristic depending on the deviation of said iirst signal from the time of occurrence of a corresponding pulse of said second series of pulse emissions, and means responsive to said second signal to control the recurrence rate of said pulse generating means to reduce said deviation.

6. A means for maintaining a recurrent first series of pulse signals in a known time relation with a similarly recurrent second series of pulse signals comprising, means for generating a timing wave to control the recurrence rate of said first series of pulse signals, means for producing a first signal of the same recurrence rate as said rst pulse signals, said signal leading a corresponding pulse of said first series by said known time relation, a time interval measuring circuit having as input signals thereto said first signal and pulses in said second series for producing a second signal having a characteristic depending on the deviation of said first signal from the time of occurrence of a corresponding pulse of said second series of pulse signals, and means responsive to said second signal for controlling the frequency of said timing wave generating means to reduce said deviation.

'7. A means for maintaining a recurrent first series of pulse emissions in a known time relation with a similarly recurrent second series of pulse emissions, comprising means for generating a timing wave to control the recurrence rate of said first series of pulse emissions, means for generating said rst series of pulse emissions in accordance with said timing wave, means for producing a first signal of the same recurrence rate as said first series, said signal leading a corresponding pulse of said rst series by said known time relation, means for receiving said second series of pulse emissions, a time interval measuring circuit coupled to said first signal generating means and said second pulse series receiving means for producing a second signal having a characteristic vdepending on the deviation of said first signal from the time of occurrence of a corresponding pulse of said second series of pulse emissions, and means-responsive to said second signal for controlling the frequency of said timing wave generating means to reduce said deviation'.

8. A circuit for maintaining a recurrent first series of pulse signals in a known time relation with a similarly recurrent second series of pulse signals comprising, means for generating said first series of lpulse signals at substantiallythe same recurrence-rate as said second series of pulse signals, means for producing a first series of narrow -pulses of the same recurrence rate as said first pulse signals, means for producing a second series of narrow pulses, each narrow pulse of said second series being spaced from a narrow pulse of said first ,series by an amount less than the pulse width of pulses in said Vsecond series of pulse signals to .produce a series of pairs of narrow pulses, each pair of narrow pulses being spaced from a corresponding pulse of the rst series of pulse signals by said known time, a iirst mixer receiving said rst series of narrow pulses and said second series of pulse signals, a second mixer receiving said second series of narrow pulses and said second series of pulse signals, the output signal of each of said mixers being a series of pulses having substantially equal amplitude when the leading and trailing narrow pulses in a pair occur symmetrically in the leading and trailing edges, respectively, of a pulse of said second series of pulse signals, first and second integrating circuits responsive to said outputs of said iirst and second mixers, respectively, each integrating circuit producing an output voltage of a magnitude proportional to the amplitude of signals from the mixer associated therewith, a differential amplifier coupled to said integrating circuits for producing a voltage proportional to the difference in magnitudes of the signals from said two integrating circuits, Vand means coupling said differential amplifier to said means for generating said first series of pulse signals to control the interval between generated pulses.

9. A circuit for maintaining a recurrent rst series of pulse signals in a known time relation with a similarly recurrent second series of pulse signals comprising, means for generating said rst series of pulse signals at substantially the same recurrence rate as said second serise of pulse signals, means for producing a third series of narrow pulses of the same recurrence rate as said first pulse signals, means for producing a fourth series of narrow pulses, each pulse of said fourth series being spaced from a pulse in said third series by an amount less than the width ofa pulse in said second series, a first mixer for combining pulses of said second and third series to produce a first signal having an amplitude dependent upon the relative time of occurrence of corresponding pulses in said second and said third series, a second mixer for combining Vpulses of said second and fourth series to produce a second signal having an amplitude dependent upon the relative time of occurrence of corresponding pulses in said second and fourth series, means for combining said first and second signals to produce a control signal of amplitude dependent on the relativeV amplitudes of said first and second signals, and means coupling said control signal to said means for generating said rst series of pulse signals to control the interval between generated pulses, said control being in a direction to equalize said first and second signals.

10. A circuit for maintaining a recurrent rst series of pulse emissions in a known time relation with a similarly recurrent second series of pulse emissions comprising, means for generating Aa timing wave to control the recurrence rate of said first series of pulse emissions, means for generating said rst series of pulse emissions in accordance with said timing wave, means for producing a rst signal of the same recurrence rate as said rst series, said rst signal comprising recurrent pairs of pulses, the midpoint in time of occurrence of each of said pairs being spaced from a corresponding pulse of said rst series by said known time, means for receiving said second series of pulse emissions, a time interval l5 Number measuring circuit coupled to said rst signal producing means and said second pulse series receiving means for producing a second signal having a characteristic depending on the deviation of said midtime of said' pairs of pulses from the time of occurrence of a corresponding pulse of said second series of pulse emissions, and means responsive to said second signal for con-V trolling the frequency of said timing wave gen- GLENN H. MUSSELIVIAN.

References Cited in the file of this patent UNITED STATES PATENTS Name Date 2,425,981 Bard et al Aug. 19, 1947 

